The term “digital image production apparatus” is understood to mean an analogue copier having page programming for print media, a digital copier or a printer. In the following text, all these apparatuses will be referred to as “printer”.
A known digital image production apparatus is disclosed in U.S. Pat. No. 5,081,595. The jobs to be printed may be scanned-in by a local operator or may be transmitted from a remote user through a network, and associated printing instructions are input by the local operator on an operating console of the printer or are also transmitted through the network. These printing instructions include a specification indicating the type of recording sheet on which the documents are to be printed. These recording sheets are distinguished not only by their size or format but also by a large variety of other parameters such as the material, e.g. paper or transparent film, the paper weight, paper color, surface finish and the like. Thus, the number of types of recording sheets which could possibly be used for printing is typically much larger than the number of trays provided in the printer.
As a consequence, a situation may occur where a job cannot be processed because the recording sheets specified by the job instructions are not available in any of the trays. Then, the user is invited to load the recording sheets that are needed for the job. In this context, the “user” does not necessarily mean the person who has entered the print job, which person may be located far away from the printer, but may also be an operator who is in charge of a printer.
It will be understood that a plurality of different types of recording sheets may be needed within one and the same print job. This is the case for example if cover sheets of the documents to be printed and/or separating sheets between them shall have a color different from the color of the other document sheets. If not all the recording sheets required for the job are available in the printer, the print processing has to be interrupted until the user or operator has loaded the required recording sheets.
The control system of the known printer includes also a scheduling software for arranging the print jobs in a print queue, if more than one job has to be processed. In this case, the user or operator may be invited to load the recording sheets needed for a subsequent print job while the print engine is processing a first job, so that the operation of the print engine does not need to be interrupted.
It may then be necessary for the operator to replace the recording sheets presently accommodated in one of the trays by another type. In order to avoid the user removing recording sheets from the print engine which are still needed for the current job or a subsequent job, the control system determines the trays which accommodate recording sheets that are needed for the scheduled print jobs, and indicates at least one or all of the other trays, i.e. the trays which may be reloaded, to the operator through the user interface.
U.S. Pat. No. 5,459,580 discloses a printer which has a sheet feeding mechanism and a register storing the type of recording sheet loaded in this sheet feeding mechanism. If the type of recording sheet specified by the job instructions is not identical with the type stored in the register, the print processing is interrupted, and the user is invited to load the required type of recording sheets. Then, after the user has loaded the required sheets and has programmed the type thereof, he must input a printing restart instruction, e.g. by pressing the start button of the printer, and the print processing is resumed.
The printers disclosed in the two U.S. patents discussed above are equipped with detectors which are able to detect the size of the sheets loaded in the various trays. However, since it would be difficult or even impossible to automatically detect also the other characteristics of the recording sheets, such as the color, the material, and the like, these characteristics have to be input manually by the user when he loads the recording sheets into one of the trays and the sheet feeding mechanism, respectively.